The present invention relates to a magnetic circuit device, and relates more particularly to a magnetic circuit device suitable for use in a magnetic catch having a switching function, a slide switch or a sensor for detecting locations of a movable member.
A prior magnetic catch is described in, for instance, U.S. Pat. No. 3,057,650. FIG. 1 is a side view of this prior magnetic catch. In this figure, a magnetic catch is composed of a flat rectangular permanent magnet 1 and a pair of flat yoke pieces 2. The magnet 1 has a pair of magnetic poles which are formed on its opposite faces. The yoke pieces 2 made of magnetic material such as iron are mounted on opposite pole faces of the magnet 1, respectively. End portions of yoke pieces 2 are projected outwardly from faces of the magnet 1 in the longitudinal direction. The magnetic catch thus arranged is mounted on a stationary part (not shown) of the door or the like. An armature piece 4 made of magnetic material such as iron is secured to a moving part 5 of the door so as to correspond to pole faces of the yoke pieces 2. With this arrangement, when the door is closed, the armature piece 4 is attracted toward pole faces of the yoke pieces 2 by the magnetomotive force resulting from the magnet 1 and bridges those pole faces, so that the door is held in a closed position. In other words, a magnetic circuit through the armature piece 4 is formed.
However, this prior magnetic catch has only the function of holding the door in the closed position. Therefore, in order to detect whether the door utilized in a copying machine for example is in the closed position or not, the use of a detecting device such as a limit switch or a micro-switch is required besides the magnetic catch. This brings about the disadvantages that parts for the detecting device must be provided independent of parts for the magnetic catch, which leads to high cost, and that a space for attaching the detecting device must be provided in addition to one for the catch.